1. Field of the Invention
This invention is directed to methods for extending the cycle life of solid, secondary electrolytic cells employing a solid electrolyte having at least about 100 ppm water and to the electrolytic cells produced by this method.
2. State of the Art
Electrolytic cells comprising an anode, a cathode and a solid, solvent-containing electrolyte are known in the art and are usually referred to as "solid electrolytic cells". One class of solid electrolytic cells are rechargeable (secondary) lithium cells which comprise a solid electrolyte interposed between an anode comprising lithium and a cathode which comprises materials suitable for recycling (recharging) the cell after discharge. The anode may be coated with a composition derived by reacting the lithium anode with from 1 to 50 weight percent water wherein the water can be initially placed into the cathode. See, for example, Masuda, et al., U.S. Pat. No. 5,057,387.
A solid, secondary battery typically comprises several solid, secondary electrolytic cells wherein the current from each of the cells is accumulated by a conventional current collector so that the total current generated by the battery is roughly the sum of the current generated from each of the individual electrolytic cells employed in the battery. Such an arrangement enhances the overall current produced by the solid, secondary battery to levels which render such batteries commercially viable.
However, one problem encountered with the use of solid, secondary electrolytic cells in such batteries is limited cycle life for the battery, i.e., the number of rechargings the battery can accept before the battery is no longer able to maintain acceptable levels of capacity. Specifically, the cycle life of the solid, secondary battery is related to the cycle lives of the individual electrolytic cells comprising the battery. In general, when one of the electrolytic cells in the battery ceases to maintain acceptable levels of capacity, the battery must drain more current from the remaining electrolytic cells so as to produce the same overall level of current from the battery which results in a reduction of the capacity of the remaining electrolytic cells in the battery. In turn, this results in a significant reduction in the cycle life of these cells and hence that of the battery.
Accordingly, in order to extend the cycle life of the battery at a given level of anodic material, it is necessary to extend the cycle lives of the individual electrolytic cells comprising the battery. It goes without saying that methods for increasing the cycle life of solid, secondary electrolytic cells would greatly facilitate their widespread commercial use.